[NLRS] 2 meter antenna elevation

Tue Jul 26 07:29:01 EDT 2011

I live in the same situation as John and have worked lots of satellites,  and 
my AOS is totally affected by the terrain, in fact by several degrees depending on the azimuth of my horizontal antenna and ofcourse where 
a particular sat. is at the time elevation wise.   When birds get to 60 or 
so degrees above horizon there is a definite signal loss and being very close to a bluff perhaps terrestrial signals act in a similar way.  At a certain distance from a bluff the incoming wave angle is steeper than the beamwidth of the antenna and gain falls off. .
 Height probably is the best method to increase gain, but I think some
experiments may be needed to verify what K0CQ is explaining.  We 
know signals will follow the curve of the earth to some extent, but I'm
not willing to discount the possible benefits of slight elevation on 2 meter and above antennas.  Maybe I'm just a hard case ignoring the facts.
 I just seems to follow that signals dropping down on the top of an antenna can't have the gain that signals from the forward direction can. 
 .   
 Hopefully I'll have a chance to do some experimenting at some point and
document the results, or if there is a study we can reference please let
us know.. The referred article is based on 6 meter studies in ideal terrain essentially...  (http://www.w9smc.com/blackhole/news%2010%2008.pdf ) and it specifically notes that the vertical beamwidth of antennas shrinks as frequency increases.  I think to answer John, we 
simply don't know.  Yet. 

73,
Dave, WV9E 
  ----- Original Message ----- 
  From: Dr. Gerald N. Johnson 
  To: nlrs at mailman.qth.net 
  Sent: Sunday, July 24, 2011 1:16 PM
  Subject: Re: [NLRS] 2 meter antenna elevation

  Digging out my 2010 CSVHF proceedings, I find the article is by W0FY on 
  pages 101-106. It is on 6m and illustrates the fine elevation pattern 
  details caused by the diffraction grating effect. Searching I find it 
  was published on line a couple years before at:
  http://www.w9smc.com/blackhole/news%2010%2008.pdf

  He found that the lowest lobe was attenuated by tilting a 6m beam, and 
  that lowest lobe was at a high enough elevation to get over W9RPM's 
  cliffs. It would be better the compute with Manna-Gal than EZNEC and to 
  use W9RPM's actual 2m beam and height because antenna height has a big 
  effect on the diffraction grating elevation pattern. I found it very 
  interesting to see that elevation pattern by listening to a satellite 
  beacon on 2m as the orbit rose or fell near vertically on a selected 
  pass. That's a good long range antenna range test.

  W9RPM's cliffs are shadowing closer station and antenna tilt isn't going 
  to help. Only much greater antenna height or moving up on top the cliffs 
  is going to help that. The longer range stations will be dropping over 
  the cliff anyway.

  Fact is VHF and UHF signals from beyond the horizon do propagate at an 
  angle. The longer range signals are refracted in the atmosphere by the 
  normal change in air density with height and that refracts rising 
  signals back down. Temperature inversions increase the refraction.

  I know on some fairly long microwave links that two antennas are 
  sometimes used at each end, one for the normal refraction and another 
  pair with greater elevation for the temperature inversion events to get 
  better reliability on a path. But those antennas probably have closer to 
  1 degree beamwidths while the practical 2m yagi is closer to 30 degrees 
  beamwidth. (And my next ones will have even greater azimuth beamwidth 
  for easier aiming.)

  73, Jerry, K0CQ

  On 7/24/2011 12:29 PM, Bruce Richardson wrote:
  >
  >
  > I was just discussing this with John on the phone and encouraged him
  > to come to the list.
  >
  > We know that a guy on the ridge does better than a guy in the valley.
  > In John's case, he really is quite close to the blocking ridge and
  > blasting right into the side of it.  Isn't it true that our 2m signals
  > get scattered by reflection and dispersion off of trees, rocks,
  > buildings, and ridges?  Doesn't this end up being forward scattered by
  > dust particles and water molecules?
  >
  > Two questions: by blasting into the side of the ridge, might he be
  > getting back-scatter that is phase cancelling some of his signal?
  > Secondly, I know curvature of the earth plays into this a bit, but I'm
  > wondering if by elevating, he might lift that main lobe above the
  > ridge and strictly work on dust particle scatter to the eastward
  > (Milwaukee and beyond).
  >
  > Dr Jerry has already replied and is kinda indicating how sharp the
  > lobe would have to be to get the intended benenfit.  Anyways,
  > interesting topic and I look forward to follow-on discussion. I'm
  > working on some graphics from RadioMobile to show the dilemma. I'll
  > post links to them when the graphics are ready. Might be tomorrow.
  >
  > 73
  > Bruce W9FZ
  >
  >
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